Had mine replaced at 78,000kms with fresh oil/pan etc. Is it good from now on or should I expect to get this done again around the 160k mark? I'd prefer to get it done proactively if it's a time-thing and avoid the potential unexpected spill/stain again.

This problem even happens on 06/07 E9x, E6X as well...the plastic pan warps as well. The gasket, sealing sleeve and hardware can be changed with just a top up. A full flush, or entire pan is usually not necessary unless you do it when the pan is hot (it will warp) or has warped already.

Definitely remind your shop of choice to inspect your trans. during your oil changes at least, catching it early will save a rebuild later on if not addressed.

I have a 2006 325xi auto, So should I mention this when I have my front brakes serviced?

If its under warranty, yes. If you are out of warranty at a dealer (first of all, I don't know why that would happen) then I'd get it checked at an Indy shop. We quote less than half of that of the dealer at our shop.